High power integrated circuits are used in a number of applications, such as power supplies, audio applications, high definition video systems, etc. A wide variety of semiconductor packages can be used for high powered integrated circuits.
Current packaging techniques for high power chips, regardless of the package type, require a large number of semiconductor processing and package manufacturing steps. In a representative manufacturing process, the back surface of the wafer is initially coated with a metal to provide both electrical grounding and thermal conductivity. The metal is usually applied by sputtering either Ti-Nickel (TiNi) or silver and tin (CrAgSn) onto the back side of the wafer. Thereafter, the individual die are singulated by sawing the wafer along the scribe lines. The die attach pad of the lead frame is often plated with silver prior to attaching the die. Eutectic solder is then used to attach the die to the pad. Wire bonding is next performed, followed by encapsulating the die in a molding material, such as epoxy. After the die is encapsulated, the underside of the package and exposed leads are plated with a tin-lead (e.g., 85% Sn 15% Pb) alloy. This layer of metal helps protect the exposed copper of the lead frame from oxidation and is compatible with the solder used to mount the package to a printed circuit board (PCB). The solder used to mount the package to the PCB is usually either a tin-silver-copper combination (e.g., 96% Sn, 3% Ag, 1% Cu) or tin-lead metal layer (e.g., 63% Sn, 37% Pb). The PCB is usually plated with a nickel-Au metal layer in the area where the package is to be mounted and often includes metal vias that thermally couple the nickel-au layer to a thermally conductive plane in the PCB board to provide a heat dissipation path away from the package.
A number of problems are associated with the aforementioned semiconductor processing and package manufacturing sequence. Foremost, a total of six layers of various metals and solders are used, between and including the metal layer sputtered onto the back surface of the wafer and the nickel-au layer on the PCB board. These layers provide a relatively poor thermal-conductive path from the die encapsulated in the package to the PCB. In addition, the use of all these layers complicate the manufacturing process and are expensive to implement.
An apparatus and method for an enhanced thermally conductive package for high powered semiconductor devices is therefore needed.